The present invention relates to a tripod type constant velocity joint used for transmission of a rotary force between rotary shafts incorporated in the driving system, for example, of an automobile and non-linearly existing therein.
Tripod type constant velocity joints are in wide use as a kind of constant velocity joint to be incorporated in the driving systems of automobiles. For example, Japanese Patent Laid-Open Publication Sho 62-233522 discloses a tripod type constant velocity joint 1 as shown in FIGS. 15 and 16. This tripod type constant velocity joint 1 comprises a hollow cylindrical housing 3 fixed to the end of a first rotary shaft 2, such as a driving shaft, and a tripod 5 fixed to the end of a second rotary shaft 4, such as the rotary shaft on the wheel side.
The inner peripheral surface of the housing 3 is formed, at circumferentially trisectional positions, with recessed grooves 6 extending axially of the housing 3. On the other hand, the tripod 5 comprises a boss 7 to be fixed to the end of the second rotary shaft 4, and columnar trunnion journals 8 radially projecting from the circumferential trisectional positions on the boss 7. Each trunnion journal 8 supports a roller 9 for rotation and more or less axial displacement through needle rollers 10. And these rollers 9 are fitted in the recessed grooves 6 in the housing 3, thereby constituting the tripod type constant velocity joint 1. In addition, a pair of guide surfaces 6a defining each recessed groove 6 are each an arcuately recessed surface, and each roller 9 is supported for rolling and swinging between these guide surfaces 6a. 
During the use of the tripod type constant velocity joint 1 constructed as described above, when, for example, the first rotary shaft 2 is rotated, its rotary force is transmitted from the housing 3 to the boss 7 of the tripod 5 successively through the rollers 9, needle rollers 10, and trunnion journals 8, rotating the second rotary shaft 4. Further, when the center axis of the first rotary shaft 2 is out of alignment with the center axis of the second rotary shaft 4, that is, when the tripod type constant velocity joint 1 takes an operating angle, with the rotation of the two rotary shafts 2 and 4, each trunnion journal 8 is displaced in a direction to swing around the axis of the tripod 5 with respect to the guide surfaces 6a of the corresponding recessed groove 6, as shown in FIGS. 15 and 16. At this time, the roller 9 supported by each trunnion journal 8 rolls on the guide surfaces 6a of the recessed groove 6 while being displaced axially of the trunnion journal 8. These movements secure equality of velocity between the first and second rotary shafts 2 and 4.
In the case of the tripod type constant velocity joint 1 constructed to act in the manner described above, when the first and second rotary shafts 2 and 4 are rotated with an operating angle taken, each roller 9 performs a complicated motion. That is, each roller 9 moves along the guide surfaces 6a while changing its direction axially of the housing 3 and is displaced axially of the trunnion journal 8. When each roller performs such complicated motion, relative displacement between the outer periphery surface of each roller 9 and the guide surfaces 6a is not necessarily smoothly effected, so that relatively large friction is generated between these surfaces. As a result, in the case of the tripod type constant velocity joint of the construction shown in FIGS. 15 and 16, a tertiary axial force is generated per revolution. And it is known that a vibration called shudder is generated in remarkable cases as when it is incorporated into an automobile to transmit a large torque with a large operating angle taken.
As measures against the above problem, French Patent No. 2752890 discloses a construction as shown in FIG. 17a and Japanese Patent Laid-Open Publication Heisei 3-172619 discloses a construction as shown in FIG. 19. The construction of FIG. 17a is such that a roller assembly (inner and outer rollers relatively rotatable through needle rollers) is parallelly guided in a recessed groove in the housing and such that centering and swinging are made possible between the spherical inner peripheral surface of the inner roller and the spherical trunnion journal, and spherical fitting is ensured in that the generating line of the outer peripheral surface of the spherical trunnion journal is an arc having a radius of curvature, rT, smaller than the radius (A/2) of the trunnion journal. In this case, the major diameter of a contact ellipse generated under a load torque between the inner roller spherical inner peripheral surface and the spherical trunnion journal becomes longer. Increasing a spherical surface clearance {(C−A)/2} makes spherical fitting possible without having to make the radius of curvature, rT, smaller than A/2. In that case, however, not only does the rotation-directional play become larger but also the contact area becomes smaller, resulting in a disadvantage leading to rotation durability decreasing with increasing contact surface pressure.
With the construction of FIG. 19, since a torque load is imposed between the cylindrical inner peripheral surface 20 of the inner roller and the spherical trunnion journal 8, the contact surface area further decreases, resulting in a disadvantage leading to rotation durability decreasing with increasing contact surface pressure. Further, the width (corresponding to the contact ellipse minor diameter) of the contact surface further decreases and the circumferential contact length corresponding to the major diameter further increases. The contact surface pressure is also high.
In these prior art tripod type constant velocity joints, a swing slip that takes place on the contact ellipse due to the swing of the trunnion journal when the joint is rotating under a load with an operating angle taken acts, as shown in FIG. 18, as a spin moment tending to change the rolling direction of the roller assembly, so that the roller assembly has its direction changed until it contacts the guide surfaces of the recessed groove in the housing, and the contact force becomes greater. Further, since it is no longer parallel with the recessed groove in the housing, it is thought that smooth rolling is impeded and the rolling resistance cannot be fully reduced.
A main object of the invention is to provide a tripod type constant velocity joint that has solved the above problems. That is, the invention is intended to provide a tripod type constant velocity joint wherein while holding small the clearance between the spherically surface-fitting inner roller and spherical trunnion journal, that is, holding the rotation-directional play small, spherical fitting (surface pressure reduced) is made possible and the contact ellipse major diameter is reduced so as to keep small the spin moment generated by the swing of the trunnion journal, so as to minimize the rolling resistance in the roller assembly during the rolling with an operating angle taken, thereby ensuring the coexistence of reduced shudder and high durability when the joint is assembled to an automobile.